Current cell towers provide free space radiation and directional antenna sectors. The required narrow antenna beams to cover only a highway cannot be realized at 698 to 2700 MHz cellular frequencies. For example, for a 10 mile long by 100 foot wide highway coverage cell, the beamwidth required is tan−1 (100/52800)=0.11 degrees, which may require a 65 dBi gain antenna hundreds of wavelengths diameter. Additionally, the resulting cell would not be rectangular, but triangular shaped and the signal strength not uniform. Other problems with towers include unreachable spaces (building interiors, tunnels, backside of hills), cannot realize a strip shaped coverage cell, will not provide road only coverage, cells cannot follow a turn in a road, limited frequency reuse, low security and too far for self powered RFID.
A single-wire transmission line (SWTL or single wire method) is a method of transmitting electrical power or signals using only a single electrical conductor. In a publication by Georg Goubau, entitled “Surface waves and their Application to Transmission Lines,” Journal of Applied Physics, Volume 21, November (1950), a surface wave mode along a wire is discussed. Electric and magnetic fields along the wire were linearly polarized, e.g. they did not rotate about the wire axis as would rotationally polarized fields.
In U.S. Pat. No. 2,685,068 entitled “Surface Wave Transmission Line” Goubau proposed the application of a dielectric layer surrounding the wire. Even a rather thin layer (relative to the wavelength) of a dielectric will reduce the propagation velocity sufficiently below the speed of light, eliminating radiation loss from a surface wave along the surface of a long straight wire. This modification also had the effect of greatly reducing the radial footprint of the electromagnetic fields surrounding the wire, addressing the other practical concern. Radiation from the wire was not for wireless communication and a separate radiating antenna was provided. The separate radiating antenna was wired to the SWTL to exchange conducted electric currents. Electric and magnetic fields along the wire were linearly polarized.
In U.S. Pat. No. 2,921,277 entitled “Launching and Receiving of Surface Waves” Goubau also proposed a method for launching (and receiving) electrical energy from such a transmission line. The Goubau line (or “G-line”) includes a single conductor coated with dielectric material. At each end is a wide disk with a hole in the center through which the transmission line passes. The disk may be the base of a cone, with its narrow end connected typically to the shield of coaxial feed line, and the transmission line itself connecting to the center conductor of the coax. Even with the reduced extent of the surrounding fields in Goubau's design, such a device only becomes practical at UHF frequencies and above. Wireless communication by wire radiation was not described.
More recently, a product has been introduced under the name “E-Line” which uses a bare (uncoated) wire, but employs the cone launchers developed by Goubau. Thus, the resulting wave velocity is not reduced by a dielectric coating, however the resulting radiation losses may be tolerable for the transmission distances intended. The intended application in this case is not power transmission but power line communication, that is, creating supplementary radio frequency channels using existing power lines for communications purposes. This has been proposed for transmission of frequencies from below 50 MHz to above 20 GHz using pre-existing single or multi-strand overhead power conductors. Communications to mobile units was not described.
For example, U.S. Pat. No. 7,009,471 entitled “Method and Apparatus for Launching a Surfacewave onto a Single Conductor Transmission Line Using a Slotted Flared Cone” to Elmore discloses an apparatus for launching a surfacewave onto a single conductor transmission line that provides a launch including a flared, continuously curving cone portion, a coaxial adapter portion, and a wire adapter portion for contacting the wire conductor which allows for a multiplicity of wire dimensions for either insulated or uninsulated wire, or a tri-axial wire adapter device enabling non-contacting coupling to a wire. A longitudinal slot is added to the flared cone, wire adapter, and coaxial adapter portions of the launch to allow direct placement of the launch onto existing lines, without requiring cutting or threading of those lines for installation.
Also, U.S. Pat. No. 7,567,154 entitled “Surface Wave Transmission System Over a Single Conductor Having E-fields Terminating Along the Conductor” to Elmore discloses a low attenuation surface wave transmission line system for launching surface waves on a bare and unconditioned conductor, such as are found in abundance in the power transmission lines of the existing power grids. The conductors within the power grid typically lack dielectric and special conditioning. A first launcher, preferably includes a mode converter and an adapter, for receiving an incident wave of electromagnetic energy and propagating a surface wave longitudinally on the power lines. The system includes at least one other launcher, and more likely a number of other launchers, spaced apart from one another along the constellation of transmission lines. The system and associated electric fields along any given conductor are radially and longitudinally symmetrical.
It may be desirable to obtain precise communications coverage areas, for frequency reuse, communications privacy, and security needs, for example, including microcellular telephone coverage, communications, especially communications to mobile units, and communications inside mines, tunnels, buildings, or hallways, or for Radio Frequency Identification Device (RFID) tracking.